In a conventional waveguide connection structure by which a waveguide (through hole) arranged in an organic dielectric substrate (connecting member) to transmit an electromagnetic wave is connected to a waveguide arranged in a metal waveguide substrate, a conductor on the through hole and the metal waveguide substrate are electrically connected to each other and are maintained at the same electric potential, so that reflection, transmission loss, and leakage of the electromagnetic wave are prevented at a connection area of the waveguides (for example, see Patent document 1).
In the conventional waveguide connection structure disclosed in Patent document 1, a gap is formed between a conductor layer on the through hole and the waveguide substrate due to warpage, or the like, of the organic dielectric substrate. As a result, there is a problem that a leaky wave in a parallel plate mode occurs between metal conductors and the reflection and the transmission loss of the electromagnetic wave becomes large at the connection area.
To improve the above-described degradation of the connection characteristics, a conventional choke structure is often employed in which a groove having a depth of λ/4 is formed at a position λ/4 away from an E-plane edge of the waveguide, and the E-plane edge of the waveguide is closed-ended in a standing wave from a closed-end point of a choke groove (for example, see Patent document 2).
Patent document 1: Japanese Patent Application Laid-open No. 2001-267814 (paragraph [0028], FIG. 1) Patent document 2: U.S. Pat. No. 3,155,923